Ion sources are used in a variety of applications, from heat treatments to physical vapor deposition (“PVD”) of materials onto workpieces. Typically, the ion source material is consumed to produce the vapor, which also results in the transmission of undesirable chunks or droplets called macroparticles. Macroparticles are undesirable for nearly all ion source applications, especially those applications involving PVD. The PVD equipment industry serves a ten billion dollar market.
Frequently, PVD techniques using an electric arc, specifically cathodic arc, are preferable over other PVD deposition methods due to the production of copious numbers of ions. The production of a highly ionized plasma combined with the use of electrically biased workpieces, may allow the arrival energy of the ions to be controlled during deposition, thereby providing for optimization of important film properties such as stoichiometry, adhesion, density, and hardness or, for example, controlling the uniform buildup of coating inside of trenches and vias on computer chips. As another example, the hardness of diamond-like-carbon (DLC) films deposited using cathodic arc evaporation have been shown to be four times harder than DLC films deposited using non-ionized methods, approaching the hardness of natural diamond. A second primary reason, in addition to high ion flux, that cathodic arc sources have been widely adopted commercially (for applications that are relatively insensitive to macroparticles, such a cutting tool coatings), is that they are relatively robust, compact and simple devices.
Notwithstanding the noted benefits of PVD using a cathodic arc, this deposition technique also produces undesirable macroparticles. These chunks or droplets of source material lead to blemishes in the coatings and exclude unfiltered or poorly filtered cathodic-arc ion sources from use in applications requiring smooth films such as optical, electronic (e.g. computer chip, battery, solar) or data storage coatings (e.g. computer hard drive). Applications less sensitive to macroparticle contamination such as cutting tool coatings have also been shown to benefit from filtered deposition because macroparticles that become incorporated into the coating can fall out during cutting operation, opening a hole through the coating, which can lead to coating failure. Furthermore, filtered, pure ion deposition produces films with properties that are superior to unfiltered cathodic arc films, providing benefits in addition to macroparticle elimination.
Despite known prior art efforts to eliminate the transmission of macroparticles, techniques of the prior art (commonly referred to as “filtering”) appear unable to eliminate macroparticles without significantly compromising the compact size, simplicity, and high flux ion production benefits of unfiltered cathodic-arc sources. Coating deposition rate, distribution area, and uniformity may be significantly reduced in prior art devices. In addition, the filtering equipment that is generally added to the cathodic arc source is typically large in size, non-symmetrical, complex and expensive to manufacture. Also, despite significant effort, at least some macroparticles may pass through prior art filters, which is a problem when extremely smooth films are required—in computer disc, electronic or optical applications, for example. This may be particularly problematic when depositing diamond-like-carbon films produced by evaporating graphite. Macroparticles produced from metal cathodes are typically liquid and do not bounce but adhere to the first surface they encounter. In contrast, macroparticles produced during the evaporation of graphite are solid, elastic and energetic, and can be reflected numerous times from surfaces within a filter. (Other materials such as silicon also produce hard, elastic macroparticles.) Even with no line-of-sight between the source material and the workpieces and the presence of baffling to catch them, elastic macroparticles, may be reflected numerous times from surfaces within a filter and reach workpieces.